1. Field of the Invention
This invention relates to a picture projector, and more particularly to a cylinder-type color wheel adaptive for providing a picture projector with a thin thickness and a fabrication method thereof. Also, the present invention is directed to a picture projector using the same.
2. Description of the Related Art
Generally, a picture projector is a device that enlarges and projects a minute picture implemented internally to display it on a large-dimension screen. In order to realize a color, the interior of such a picture projector is provided with a color wheel for separating red (R), green (G) and blue (B) colors on a time basis. The color wheel is rotated by a rotation of a motor to separate a color sequentially.
FIG. 1A and FIG. 1B show a conventional color wheel. Referring to FIGS. 1A and 1B, the conventional color wheel 10 includes a color filter 6 for transmitting only a light beam with a wavelength corresponding to each color in a white light beam, a coupler 4 to which the color filter 6 is attached, and a motor 2 to which the coupler 4 is attached. The color filter 6 consists of a red color filter 6R for transmitting only a light beam corresponding to a red color in a white light beam, a green color filter 6G for transmitting only a light beam corresponding to a green color in a white light beam, and a blue color filter 6B for transmitting only a light beam corresponding to a blue color in a white light beam. The color filter 6 is attached to the coupler 4 by an adhesive, and the coupler 4 is attached to the motor 2 by way of holes 5 provided at the inner side thereof. In other words, the color filter 6 is rotated by a driving force of the motor 2 to sequentially separate a color.
FIG. 2 shows a conventional picture projector in which the color wheel is installed at the interior thereof. Referring to FIG. 2, the conventional picture projector includes a lamp 12 for generating a light beam, a reflector 14 for reflecting a light beam into the front direction of the lamp 12, a first illuminating lens 16 for narrowing a width of a light beam reflected from the reflector 14, a color wheel 10 for transmitting only a specific color light of a light beam, a field diaphragm 22 for shutting off a spurious light beam in a light beam passing through the color wheel 10, second and third illuminating lenses 18 and 20 for narrowing a width of a divergent light beam passing through the field diaphragm 22, a full-reflective mirror 26 for reflecting a light beam passing through the second and third illuminating lenses 18 and 20 in a specific direction, a fourth illuminating lens 28 for converging a light beam reflected from the full-reflective mirror 26 to apply it to a reflective picture display device 30, a reflective picture display device 30 for reflecting a light beam from the fourth illuminating lens 28 in accordance with an image signal to realize a picture beam, and a projecting lens 32 for enlarging and projecting the picture beam realized at the reflective picture display device 30 at a certain distance. A light beam generated from the lamp 12 is focused to the color filter 6 of the color wheel 10 by means of the reflector 14. The first illuminating lens 16 narrows a width of the light beam so that all the light beam focused to the color filter 6 by the reflector 14 can pass through the color filter 6. The color filter 6 is rotated by a driving force of the motor to sequentially transmit red (R), green (G) and blue (B) color lights. A light beam departing a desired light width in light beams passing through the color filter 6 is eliminated by the field diaphragm 22. The light beam passing through the field diaphragm 22 diverges beyond a focus length of the first illuminating lens 16. The second and third illuminating lenses 18 and 20 narrow a width of the light beam so that all the light beam diverging beyond a focus length of the first illuminating lens 16 can be incident to the full-reflective mirror 26. The full-reflective mirror 26 reflects a light beam incident to itself to apply it the fourth illuminating lens 28. The fourth illuminating lens 28 converges a light beam from the full-reflective mirror 26 into the reflective picture display device 30. The reflective picture display device 30 reflects a light beam inputted from the fourth illuminating lens 28 in accordance with an image signal to generate a picture beam carried with a picture information and transfers the picture beam to the projecting lens 32. The projecting lens 32 enlarges the picture beam to transmit the enlarged picture beam onto a screen installed ahead certain distance.
However, the conventional picture projector having the configuration as mentioned above has a problem in that, since only the first illuminating lens 16 is used to input a light beam to the field diaphragm 22, a light beam is converged into the center thereof to have a non-uniform light distribution caused by an increase in a light amount, thereby deteriorating a brightness uniformity of a picture. In order to solve this problem, a picture projector as shown in FIG. 3 has been used.
Referring to FIG. 3, the conventional picture projector includes a lamp 40 for generating a light beam, a reflector 42 for reflecting a light beam into the front direction of the lamp 40, a color wheel 10 for transmitting only a specific color light of the light beam, a road lens 44 for making a uniform light distribution of a light beam passing through the color wheel 10, a collimator lens 46 for progressing a light beam passing through the road lens 44 in parallel, a beam splitter 48 for transmitting a light beam inputted from the collimator lens 46 and reflecting a light beam inputted from a picture display device 50, a picture display device 50 for reflecting a light beam from the collimator lens 46 in accordance with an image signal to display a picture, and a projecting lens 52 for enlarging and projecting a picture beam inputted from the picture display device 50 at a certain distance. A light beam generated from the lamp 40 is focused to the color filter 6 of the color wheel 10 by means of the reflector 42. The color filter 6 is rotated by a driving force of a motor 2 to sequentially transmit red (R), green (G) and blue (B) color lights. The light beam color-separated by the color wheel 10 is incident to the road lens 44. The road lens 44 uniforms a light beam so that the light beam may be uniformly distributed on a screen. A light beam passing through the road lens 44 is progressed to the picture display device 50 in parallel by means of the collimator lens 46. At this time, the light beam progressing from the collimator lens 46 into the picture display device 50 transmits the beam splitter 48. The picture display device 50 reflects a light beam inputted from the collimator lens 46 in accordance with an image signal to generate a picture beam carried with a picture information and transfers the picture beam to the beam splitter 48. The beam splitter 4832 reflects the picture beam from the picture display device 50 into the projecting lens 52. The projecting lens 52 enlarges the picture beam to transmit the enlarged picture beam onto a screen provided ahead certain distance.
In the conventional picture projector as shown in FIG. 2 or FIG. 3, it is desirable that, when a light beam passes through the color wheel 10, the light beam should pass through a boundary portions of the color filter at a minimum time. In other words, a light beam is shut off when it passes through the boundary portions of the color filter 6. For instance, assuming that the motor is rotated at a speed of 3600 RPM so as to display a field of 60 times per second, a time when a light beam passes through the boundaries will be calculated. In this case, it is assumed that, as shown in FIG. 4, a light beam is a square having a size of 8 mm in width and 6 mm in length, and an inner radius of the color wheel 10 is 30 mm and an outer radius thereof is 40 mm. An angle when the light beam passes through a certain surface of the color filter 6 is given by the following equation.                     θ        =                              2            xc3x97                          arctan              ⁡                              (                                  3                  31                                )                                              =                      11.055            o                                              (        1        )            
wherein 31 are a distance from the center of the color wheel 10 until the light beam, and 3 is a half value of the length of the light beam. A time when the light beam passes the boundary portions 7 of the color filter 6 is given by the following equation.                     t        =                                            1              60                        xc3x97                          11.055              120                                =                      1.54            ⁢                          xe2x80x83                        ⁢            μ            ⁢                          xe2x80x83                        ⁢            s                                              (        2        )            
wherein 120 is a value of dividing 360xc2x0 by 3 (i.e., the number of boundary portions 7). As seen from the equation (2), a time of 1.54 xcexcs is required when the light beam passes through the boundary portions 7 of the color filter 6.
As seen from the above equations (1) and (2), it is necessary to enlarge an inner radius of the color so as to shorten a time when the light beam passes through the boundaries 7 of the color filter 6. However, the conventional picture projector has a problem in that, as an inner radius of the color wheel 10 goes larger, both a size and a weight of the is more increased. Also, the conventional color wheel 10 can not be installed to overlap with an optical system (i.e., various lenses). In other words, the conventional color wheel 10 should be installed such that it can not be interfered with an optical system. For this reason, a large space is required to install the color wheel 10. In order to solve such a problem, there has been suggested a funnel-shaped color wheel 54 as shown in FIG. 5.
Referring to FIG. 5, the funnel-shaped color wheel 54 includes a body 56, a color filter 62 attached to the body 56 to transmit only a light beam with a wavelength corresponding to each color in a white light beam, and a motor 58 to which the body 56 is attached. The color filter 62 consists of a red color filter 62R, a green color filter 62G and a blue color filter 62B for transmitting only any one of red, green and blue light beams, respectively. The color filter 62 is attached to the funnel-shaped body 56, and the body 56 is attached to the motor 58. The color filter 62 is rotated by a driving force of the motor 58 to sequentially separate a color.
FIG. 6 shows a picture projector in which a funnel-shaped color wheel is installed at the interior thereof. Referring to FIG. 6, the conventional picture projector provided with a funnel-shaped color wheel includes a lamp 64 for generating a light beam, a reflector 66 for reflecting a light beam into the front direction of the lamp 64, a color wheel 54 for transmitting only a specific color light of the light beam, a road lens 68 for making a uniform light distribution of a light beam passing through the color wheel 54, an objective lens 70 for focusing a light beam passing through the road lens 68, a collimator lens 72 for progressing a light beam diverging beyond a focus length of the objective lens 70 in parallel, a beam splitter 74 for transmitting a light beam inputted from the collimator lens 72 and reflecting a light beam inputted from a picture display device 76, a picture display device 76 for reflecting a light beam from the collimator lens 72 in accordance with an image signal to display a picture, and a projecting lens 78 for enlarging and projecting a picture beam inputted from the picture display device 76 at a certain distance. In a picture projector provided with the funnel-shaped color wheel 54, the color wheel 54 and the road lens 68 overlap with each other by a desired portion to improve a space utility. However, since such a funnel-shaped color wheel 54 has boundary portions 63 shaped in an oblique line, it is not easy to utilize the boundary portion.
FIGS. 7A to 7C shows a method of fabricating the conventional color wheel. Referring to FIG. 7A, first, a sheet 80 is coated with a red dye so as to product a red color filter 6R. At this time, if it is intended to product a green color filter 6G, the sheet 80 is coated with a green dye; and if it is intended to product a blue color filter 6B, the sheet 80 is coated with a blue dye. After the sheet 80 was coated, the sheet 80 is cut away in compliance with a size of the color filter 6R as shown in FIG. 7B. The color filter 6R cut from the sheet 80 is attached to the coupler 4 by an adhesive as shown in FIG. 7C, and the coupler 4 is attached to the motor 2 by way of the holes 5 provided at the interior thereof. The color filter 6 is rotated by a driving force of the motor 2 to sequentially separate a color. In such a method of fabricating the conventional color wheel 10, the color filter 6 is attached to the coupler 4 by an adhesive. However, since an adhesive force of the adhesive has a limit, the color filter 6 may be separated due to a centrifugal force generated upon rotation of the motor 2. Also, the color filter 6 has been from the sheet 8. Accordingly, the color filters 6R, 6G and 6B have a minute difference in shape. If the color filters 6R, 6G and 6B attached to the coupler 4 have a non-uniform shape, then a trembling of the coupler 4 and/or a noise is generated upon rotation of the motor.
Accordingly, it is an object of the present invention to provide a cylindrical color wheel that is adaptive for making a slim-type picture projector, a fabricating method thereof, and a picture projector employing the same.
In order to achieve these and other objects of the invention, a cylindrical color wheel according to one aspect of the present invention includes a color drum in which a plurality of color filters for transmitting only a light beam having a wavelength corresponding to a different color is integrally formed in a cylinder shape; a coupler to which the color drum is attached; and a motor for rotating the coupler to which the color drum is attached.
A picture projector employing a cylindrical color wheel according to another aspect of the present invention includes a light source for generating a light beam; a first optical device for focusing a light beam inputted from the light source; a second optical device for making a uniform light distribution of the light beam focused at the first optical device; said cylindrical color wheel being integrally formed, in a cylinder shape, with a plurality of color filters to sequentially separate a color light from the light beam inputted from the second optical device; a picture display device for taking advantage of the color light to display a picture according to an image signal; and a projecting lens for enlarging and projecting the picture.
A picture projector employing a cylindrical color wheel according to still another aspect of the present invention includes a light source for generating a light beam; a reflector for reflecting the light beam into the front direction of the lamp; said cylindrical color wheel for sequentially separating and transmitting a color light from the light beam reflected from the reflector; a road lens for making a uniform light distribution of the color light; a collimator lens for progressing the light beam inputted from the road lens in parallel; a picture display device for taking advantage of the color light inputted from the collimator lens to generate a picture beam according to an image signal; a beam splitter, being provided between the collimator lens and the picture display device, for transmitting the color light inputted from the collimator lens and reflecting the picture beam inputted from the picture display device; and a projecting lens for enlarging and projecting the picture beam.
A method of fabricating a cylindrical color wheel according to still another aspect of the present invention includes the steps of coating red, green and blue dyes on the surface of a transparent cylinder-shaped tube; cutting away the transparent cylinder-shaped tube coated with the dyes; attaching the cut-away cylinder-shaped tube to a coupler; and attaching the coupler to a motor.
A method of fabricating a cylindrical color wheel according to still another aspect of the present invention includes the steps of coating red, green and blue dyes on a transparent thin film; cutting away the thin film coated with the dyes; winding the cut-away thin film in a drum shape; attaching the drum-shaped thin film to a coupler; and attaching the coupler to a motor.